Bath Mat Recommendations

Hi All - I have a very sizable 9-month old and we have been using the Frida Grow-With-Me bath tub that has a 3 position "sling" mat for their changing support needs as they grow. Well, we're to the point where little man doesn't fit in it, but the bottom is too slippery to just let him go in there without something. Anyone have any recommendations for cut-to-size bath mats that aren't permanent so we can clean it off to avoid slime/mildew etc.? Google keeps just giving me other tubs to use, and the mats are for the full tub which we're not ready for just yet. Something that isn't made with harsh materials that can be cut to size and removable. Thanks in advance!